The invention relates to a method for the cylinder-specific determination of the injected fuel quantity in a multicylinder internal combustion engine and to an apparatus for controlling the cylinder-specific fuel injection quantity. In the present context, the term “cylinder” is used to indicate any types of combustion chamber of internal combustion engines.
In multi-cylinder internal combustion engines with cylinder-specific fuel injection, it is necessary to set a defined fuel/air mix for each cylinder, generally as far as possible the same mix, i.e. with the same air/fuel ratio or lambda value, for all the cylinders. In this context, however, different mixes may be formed in the individual cylinders even if the formation of identical mixes is actually intended, for example on account of manufacturing tolerances and different ageing properties of injection nozzles assigned to the individual cylinders and on account of differences in the air mass which is drawn in for the respective cylinder. Corresponding adaptive control of the injected fuel quantity is expedient in order to compensate for these effects.
To achieve mixes which are as uniform as possible in the individual cylinders of an internal combustion engine, it is known for the combustion air ratio, i.e. the lambda value, in the exhaust gas of the internal combustion engine to be measured on a time-resolved basis by means of a lambda sensor, and for the quantity of fuel injected into the respective cylinder to be controlled on the basis of the measurement signal from this lambda sensor. On account of the slow response of lambda sensors, with typical reaction times of not significantly below 100 ms, with this procedure it is relatively difficult to use the measured lambda values to ascertain the cylinder-specific deviations in the injected fuel quantity and to assign these deviations to the individual cylinders. Moreover, it is almost impossible to correctly identify the cause of control deviations, i.e. whether they are caused, for example, by different injected fuel quantities or different intake air masses.
It is the object of the present invention to provide a method for the cylinder-specific determination of a fuel injection quantity as well as an associated method and apparatus for the cylinder-specific control of the fuel injection quantity, which, with relatively little outlay, allow comparatively accurate cylinder-specific determination of the fuel injection quantity and correspondingly accurate control of the fuel quantity being injected into each cylinder.